I am new to homebreweing and i currently have three 6.5 gallon fermenters with lids and airlocks, but i have yet to acquire a carboy. Will these be as effective for secondary fermentation? Is it still worth it to do a secondary fermentation with a bucket?

Long term storage in a plastic bucket could be bad for your beer. Plastic is permeable to oxygen and would eventually let it into your beer and oxidize it. Now, having said that, I use a plastic conical and all my lagers are in there roughly a month before I keg them with no oxidized defects. Also remember the main purpose of a secondary is to allow your beer some clearing time and to get it off the primary yeast cake/trub. If you bottle this will result in less sediment. I think you'll be fine...just minimize the total time it's in a plastic bucket. Now, if you were going to lager it for 6 months then I'd suggest glass or stainless steel.

I myself am an Ale brewer as I don't have the equipment or the patients for lagers. I use the 1-2-3 rule supplemented with my hydrometer to validate fermentation being complete.
1-week in primary
2-weeks in secondary
3-weeks bottle conditioning

When I first started brewing I didn't have carboys either, and I used plastic buckets with lids / airlocks for 2 week secondary ... My advice is GO FOR IT ... until you can afford / acquire a carboy ... you'll be better off secondarying in plastic than not at all. I agree with James and Billy.